1. Field of the Invention
The invention relates to an intervertebral spacer that is inserted between vertebrae, after an intervertebral disk is previously removed, to thereby be put into contact in almost whole area with an end plate of the vertebra.
2. Description of the Related Art
There have been known intervertebral spacers inserted between the vertebrae the intervertebral disk of which is removed. Japanese Patent Application Laid-Open No. 2002-95685 (hereinafter referred to as a related art) shown in FIGS. 1A to 1C discloses one example of conventional intervertebral spacers.
As shown in FIG. 1A, a thickness of a rear side 101 of an intervertebral spacers 100 is larger than that of a front side 103 of an intervertebral spacers 100. An upper surface 105U and a lower surface 105L of the intervertebral spacers 100 are slanting each other, and are flat planes. Each of the slanting upper and lower surfaces 105U and 105L has a plurality of conical protruding portions 107. The intervertebral spacer 100, as shown in FIGS. 1B and 1C, is inserted between vertebrae 109A and 109B from a posterior side after an intervertebral disk is removed.
In the related art, the protruding portions 107 enhance an effect of preventing the intervertebral spacer 100 from coming off. However, the intervertebral spacer 100 has the following problems: since the front side 103 of the spacer 100 is thicker than that of the rear side 101, when the intervertebral spacer 100 is inserted between the upper and lower vertebrae 109A and 109B, it is hard to insert; further, since the upper and lower surfaces 105U and 105L are slanting each other, the end plates of the upper and lower vertebrae 109A and 109B are not put into whole surface contact with the upper and lower surfaces 105U and 105L. Hence, the contact area between them becomes small, so that the intervertebral spacer 100 can not sufficiently fix the vertebrae 109a and 109B.